Tier1 21-1/2 x 23-3/8 x 1 Carbon Pleated Air Filters offer superior air filtration and efficiency. The Merv 8 Carbon Air Filters are constructed with electrostatically charged, 100% synthetic Kimberly Clark media which provides significantly higher particulate efficiency than regular poly/cotton media pleated filters, with little change in static pressure. Airborne odors such as smoke, pet odors, and cooking odors are absorbed by the activated carbon pores laced into the filter media of the air filter. The Tier1 Air Filters capture airborne particles/allergens between 1 and 10 microns, such as particles that carry viruses and bacteria, pollen, mold spores, fine dust and pet dander. The Merv 8 Pleated Filter will last up to 3 months depending on your air quality! These air filters are environmentally friendly because the media is free of ink, dyes, resin, and contains no adhesives, binders, chemicals or additives. Use of water based adhesives containing no volatile organic compounds (VOCs), and minimum use of ink on the perimeter of the filter, make these air filters eco-friendly. This filter is comparable to the 3M Filtrete Ultra Allergen Series in performance. The Tier1 Air Filters provide equipment protection. This product is listed and rated by Underwriters Laboratories as U.L. Class 2. 6-pack of air filters.